Slightly confused at starter cord locking up.

[Darkslider]

I've got two top handles that both have the same problem, an Echo CS350tes and a Husky T525. Bought them both second hand and they've both done this since I got them, I'm focusing on the Husky at the mo as that's the one I want to use more often.

 

Starter frequently (i.e every 3 pulls) locks up absolutely solid, making life very difficult up a tree. I've rebuilt a 200t that has 200 psi compression and have a 372 with no decompressor and this is harder to start than both of them so it's not just a case of MTFU.

 

Piston looks good exhaust is clear as is the flywheel to coil gap. With the plug removed it pulls over lovely and freely no sign of any nipping up or seizing, and once running it's perfect with stable idle and loads of power. But refit the plug and it's back to locking up solid again.

 

Immediate thought is it feels like it has stupid high compression, maybe been run oily or with a blocked filter and coked up the cylinder/piston crown. However I tried my motorcycle compression tester on it (Sealey MS100, only one I have which has a 10mm plug adapter) and even after 30 hard pulls (10 of which were of the seized type) the best I could get was 90 psi.

 

If my compression tester is to be trusted which I think it is as it should be designed for 50cc 2 stroke scooters,  then this isn't making much sense. The only thing I can think of causing this issue is a coked up cylinder ramping the compression up, but the reading on the gauge suggests it's knackered and needs a new pot and piston. 

 

Any suggestions gratefully received!

[pleasant]

Incorrect plug length? Flooding due to low compression and hydraulic lock? Is the plug wet through when you remove it? That's where I would start.

 

Bit confused where you state 'and even after 30 hard pulls (10 of which were of the seized type) the best I could get was 90 psi' It's either 'seized' or you can pull it over...if it's seized, then it's seized...if you can pull it over albeit with increasing difficulty, then it's not seized...which is it?

[Darkslider]

 

2 hours ago, pleasant said:

Incorrect plug length? Flooding due to low compression and hydraulic lock? Is the plug wet through when you remove it? That's where I would start.

 

 

 

Plug is the correct one for the saw as I replaced it when the saw came to me, it exhibits the same behaviour with a compression tester fitted in place of the plug too. 

 

The carb leaking fuel into the cylinder raising the compression was also one of my thoughts but the plug isn't sopping when I remove it, it's the same when pulled over with the throttle wide open too. I tried filling the cylinder with contact cleaner and giving it a few pulls to clean it out but no change there.

 

[quote]

Bit confused where you state 'and even after 30 hard pulls (10 of which were of the seized type) the best I could get was 90 psi' It's either 'seized' or you can pull it over...if it's seized, then it's seized...if you can pull it over albeit with increasing difficulty, then it's not seized...which is it?

[/quote]

 

This is exactly the confusion, you get two normal pulls then the third locks up solid, let the cord retract a little and give it a monster tug and it pulls through and then you get another 2 pulls and so on. So it's obviously not seized, but every 3rd or 4th pull it's behaving like it is.

 

I think my next step is to try it with the fuel line disconnected from the carb just to rule that out, then it might have to go to the dealer for a known good compression test to confirm my testers result is accurate 

Edited October 20, 2022 by Darkslider

[pleasant]

Banana conrod?

[Darkslider]

17 minutes ago, pleasant said:

Banana conrod?

Hope not, it's a possibility though! Think I'll get a 100% confirmed compression reading from somewhere first then take it to bits if it agrees with my tester

[Will C]

have you got access to a bore scope? I found the end of a plastic piston stop on the top of a piston once that made a saw bind up every so often. You may be able to see through the exhaust port.

 

other thought is have you taken the starter cord side cover off? Unusual but could be something amis in there that is binding 🤔

 

 

[pleasant]

13 minutes ago, Will C said:

have you got access to a bore scope? I found the end of a plastic piston stop on the top of a piston once that made a saw bind up every so often. You may be able to see through the exhaust port.

 

other thought is have you taken the starter cord side cover off? Unusual but could be something amis in there that is binding 🤔

 

 

Did say they had taken it off to check the air gap on the coil.

[Will C]

45 minutes ago, pleasant said:

Did say they had taken it off to check the air gap on the coil.

I missed that 🤦‍♂️

[Darkslider]

And remember it pulls over dead easily forever with no plug in, the problems only there when it's got the plug in and building compression which makes me think it's gotta be something in the cylinder causing it, just can't for the love of me think what

[pleasant]

Well, it won't be carbon build up, because if it were then you would have the same issue with or without the plug fitted- removing the plug won't remove the carbon, so you can disregard that you said it might be earlier on.

 

Re-fitting the plug is causing pressure within the engine due to compression- this could highlight a slight bend in the conrod (as I mentioned earlier) particularly as you don't know the history. If the previous owner has messed about removing the clutch or flywheel and it was particularly tight to remove, then 'locking' the piston from moving can easily bend a conrod- or a bent crank or failing bearing, which without pressure applied will rotate 'loosely but still in a circular motion-however will 'collapse' under any pressure 'load' if the race is worn so allowing the crank to rotate 'off centre' during pulling of the recoil

Edited October 20, 2022 by pleasant